Method of preparing sodium soap thickened greases



@et 2l, 1969 H. J. PITMAN ETAL METHOD OF PREPARING SODIUM SOAP THICKENED GREASES Filed June 29, 196e lahm;

United States Patent O 3,474,034 METHUD F PREPARHN G SODlIUM SOAP THICKENED GREASES Herbert li. Pitman, Nederland, Tex., and Clarence L. Dowden, Jr., Wilton, Conn., assignors to Texaco Inc.,

New York, N.Y., a corporation of Delaware Filed .lune 29, 1966, Ser. No. 561,444

Tnt. Cl. Crn 5/12 U.S. Cl. 252-42 7 Claims ABSTRACT 0F THE DISCLUSURE A mixture of saponiiiable fatty acid material and lubricating oil is continuously oxidized in a tubular reactor under turbulent flow conditions in the presence of an oxygen-containing gas and controlled conditions of temperature and pressure to produce a product having increased viscosity which upon subsequent saponication yields a sodium-soap, wheel-bearing grease of high quality. Substantial savings in time are achieved as compared with known batch and other continuous preparation proc- CSSBS.

This invention relates to improvements in grease manufacture. It relates particularly to improvements in the oxidation of mixtures of saponiable materials and lubricating oil prior to saponiiication in a grease making process. More particularly, these improvements are directed to the continuous oxidation of a mixture of lubricating oil and saponir'iable materials.

A good wheel bearing grease must combine the properties of a high dropping7 point and proper texture with stability against texture change in service. The proper texture for greases for this type of service is a smooth short fiber texture with just the right amount of fiber development, since greases of a buttery texture are thrown off the bearings at high speed revolutions and greases of long ber or stringy texture tend to rope and feed out of the bearings. Greases which are too fibrous have a tendency to be dry and are deficient in the adhesiveness and lubricating qualities necessary in -a good wheel bearing grease.

It is known that sodium soap base greases having the texture and other properties required of a superior wheel bearing grease are obtained by carrying out a limited oxidation of a saponifiable material comprising a fatty acid glyceride and a high proportion of free fatty acid, in admixture with a minor amount of a mineral lubricating oil forming the oil component of the grease. The oxidized mixture is thereafter saponilied and dehydrated at a ternperature below the melting point of the soap, and additional mineral lubricating oil is added following the dehydration and during the cooling process. A grease preparation method which includes such an oxidation treatment is disclosed, for example, in Nelsons U.S. 2,916,453.

Oxidation treatments have also been employed heretofore in grease-making processes of other types in order to obtain different effects. For example, Kaufmans U.S. 1,996,821, U.S. 1,971,750, U.S. 2,002,819 and U.S. 2,084,974 prepared block greases of relatively low soap contents of the required hardness by heating mixtures of tallow or tallow together with a small amount of free fatty acid and the mineral lubricating oil component of the grease in the presence of air for periods up to `about 40 hours prior to saponifying the oxidized mass at a high temperature.

Continuous processes for the manufacture of lubricating greases are also known. Processes commercially employed carry out the steps of dispersing the soap in the oil, cooling, and milling the grease in a continuous stream.

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ln most cases, however, the soap is manufactured batchwise or is employed as a preformed material. Most of these processes employ a single soap and preferably do not make a great variety of formulations in one plant.

A process for the continuous production of sodium soap base lubricating greases was disclosed in Lauers U.S. 1,912,001. Another was described in Zimmers U.S. 2,383,904. Neither of these continuous processes, however, employed an oxidation step prior to the saponication operation. Kaufmans U.S. 2,084,974 discloses such a continuous process. In Kaufmans method, the first step consists of passing a mixture of mineral oil and fatty oil through a heating coil in the presence of air. The mixture is discharged into an enlarged zone where it is further blown with air while a temperature above the melting point of the final product is maintained. This oxidation step produces a viscosity increase in the oil-fat blend. When the viscosity of the mixture has reached the desired point, the blend is withdrawn from the enlarged zone and saponified while being passed through another high temperature heating coil. A flashing process which follows produces the finished grease product. The oxidation treatment employed in Kaufmans process although conducted continuously requires a residence time of 4 to 8 hours in the baffled oxidation chamber. This, however, is a substantial improvement over the seven to twelve hours of air blowing required to perform the oxidation in a batch kettle.

It is an object of the present invention to provide a process for continuously oxidizing a mixture of mineral lubricating oil and saponiable material. Another object of this invention is to provide a process for continuously oxidizing the feed stock for a sodium soap wheel bearing grease of high quality with low cost equipment in a relatively short time and with a relatively low manufacturing investment.

We have discovered that these and other objects may be achieved by making certain improvements in the processes of Kaufman and Nelson. Specifically, We have discovered that the time required to produce the desired degree of oxidation can be effectively reduced by passing a mixture of mineral lubricating oil and s-aponiable material through a tubular reactor under turbulent flow conditions in the presence of an oxygen-containing gas under controlled conditions of temperature and pressure.

In characterizing the flow quality of the gas and liquid phases in the tubular reactor we utilize a Reynolds number for each phase based on superficial velocity. Superficial velocity is computed by assuming that each phase is iiowing alone through the reactor. Therefore the term turbulent flow conditions as used herein to describe two phase flow means that the Reynolds number, based on superficial velocity, for each phase is in excess of 2000. See, Perrys Chemical Engineers Handbook, Two Phase Flow, 5-38 (4th ed. 1963).

The method of our invention can produce an oxidized mixture of mineral lubricating oil and saponifiable material on a continuous basis. It therefore is particularly suited for use in conjunction with a continuous process for the preparation of sodium soap thickened greases. One such continuous grease process with which our invention may be incorporated is the subject of a commonly assigned and copending application S.N. 333,164, filed Dec. 24, 1963, and now abandoned. This application discloses a process comprising saponication, dehydration and soap conditioning steps carried out in a continuous manner. Ideally, the product produced by our invention serves as the feedstock for this grease process, flowing continuously from the equipment used to practice our invention into the first processing sequence of the grease manufacturing facilities.

Our invention may be understood from the following detailed description, taken with reference to the accompanying drawing which illustrates diagrammatically a preferred embodiment of apparatus for practicing the method of our invention:

Vessel contains a mixture of saponiable material and lubricating oil. Charge pump 12 continuously withdraws the mixture from vessel 10 and delivers it by means of lines 11 and 13 to charge heater 14 where it is heated to the desired reaction temperature. The heated mixture then Hows through line 15 into flash chamber 17. The mixture of mineral lubricating oil and saponiable material is oxidized by recycling the material under turbulent flow conditions in the presence of an oxygen-containing gas. This is accomplished by using pump 18 to withdraw the mixture from flash chamber 17, pass it through tubular reactor 21 and return it to the ash chamber. The oxygen-containing gas is introduced by means of line 19 into line 20 of this recycle circuit at a point between pump 18 and tubular reactor 21. Excess oxygen and gases are removed from flash chamber 17 through line 25. A steam ejector and condenser, although not shown, are satisfactory for this purpose. The pressure in tubular reactor 21 and line 15 is maintained above that of the ash chambers vapor space. Back pressure regulating valves 16 and 23 in lines 1S and 22, respectively, maintain this elevated pressure in the respective lines. Pump 18 circulates the mixture through the tubular reactor at a rate which is greater than the rate of ow in line 15. A recycle rate of l0 to 200 times the feed rate has been found satisfactory in most instances.

The temperature of the tubular reactor 21 is controlled by introducing heat transfer medium into jacket 33 through line 34 and controlling the flow of heat transfer medium through the jacket by control valve 36 on line 35. It may, therefore, serve as either a heating or cooling medium, depending upon the degree of oxidation being attained in the tubular reactor.

A sidestream of oxidized product is continuously removed by means of line 26 from line 20 `between the discharge of pump 1S and the point of gas injection. The product flows through line 26 and is cooled by heat exchanger 28. Where the oxidized mixture will flow directly into grease manufacturing equipment, cooling by heat exchanger 2S is unnecessary, The viscosity of the oxidized mixture is measured by removing a sidestream of the product from line 29. The sample stream flows through line 30 into viscosimeter 31 and returns to product line 29 through line 32.

This process is readily adaptable to automatic control. Level controller 24 on ash chamber 17 regulates the control valve 27 so as to maintain a substantially constant level in the flash chamber. Preferably, a signal from viscosimeter 31 is used to provide a cascade mode of control of the temperature of the tubular reactor 21 by controlling the ow of the heat transfer medium through control valve 36. Accurate quality control of the process is achieved by this method. Optionally, it is also possible to use a signal from viscosimeter 31 to provide cascade control mode for the level controller or to control the rate of gas injection into the tubular reactor to achieve some measure of quality control.

The product from this improved process is particularly useful in making greases for the lubrication of anti-friction bearings in automobiles, buses, trucks and heavy industrial equipment. Sodium soap greases of this type, with soap contents in the range of l0 to 20% by Weight, have penetrations in the range required for Nos. 2 and 3 NLGI grade greases and dropping points in the S-450 F. range.

The saponifiable fatty acid material employed in this invention comprises a mixture of higher fatty acid glycerides and free higher fatty acids wherein the free fatty acid content is about 40 to 80% by weight of the saponifiable material. Preferably, the free fatty acid content is about S0 to 70% by weight. The fatty acids and fatty acid glycerides comprising the saponiiiable material may be any of the higher fatty acids and glycerides thereof which are employed conventionally in grease making, particularly fatty acids containing about 14 to 24 carbon atoms per molecule, preferably 16 to 18 carbon atoms, and the glycerides of such acids. The saponiiiable material should contain sufficient unsaturated fatty acid material to give an iodine value of about 30 to 80 and preferably in the range of 40 to 70. Tallow is a particularly useful saponifiable material.

The minei'al lubricating oils of the mixture serving as the feed stock for this improved process may Ibe either distillate or residual fractions from parainic, naphthenic or mixed crude bases, having viscosities in about the range 25 to 500 seconds Saybolt Universal at 210 F., preferably to 300 SSU/2l0 and more particularly 150 to 200 SSU/210.

The mixture to be oxidized comprises the saponiable material as described above and the mineral lubricating oil in an amount suicient to impart fluidity to the mass during the oxidation operation. The mixture preferably comprises a saponifiable material and mineral lubricating oil in a proportion of about 2:1 to 1:2 by weight. A residual oil having a viscosity in about the range of 100 to 300 seconds Saybolt Universal at 210 F. is particularly useful. When the combination of tallow and the preferred residual oil are employed in this improved process, u weight ratio of 1:1 has been found to be particularly useful.

The oxidation of the mixture of saponifiable material and lubricating oil need only be a limited oxidation to impart the desirable properties to the grease which is prepared subsequently. This oxidation is accompanied by an increase in viscosity which serves as a measure of the oxidation obtained. The viscosity increase is often 5-35 seconds, sometimes limited to 10-20 seconds, as measured Iby the Saybolt universal scale at 210 F.

The mixture in vessel 10 is maintained at a temperature sufficient to maintain the saponiable material in solution and to impart sufficient pumpability to the mixture. The sizes of the vessels, piping, pumping equipment, necessary controls and attendant facilities are dependent upon the feed stock, the necessary degree of oxidation and the desired production rate. It is anticipated, however, that flow rates in the range of 0.5 to 5.0 gpm. of feed and product will provide sufficient material for most greasemaking processes.

Some of the equipment sizes can be specified in general terms. For example, flash chamber 17 should be large enough to provide adequate vapor space for gas disengagement and removal following the return of the mixture from reaction in the tubular reactor. The liquid level should be high enough to provide an adequate head on the suction side of the recycle pump 18. Charge preheater 14 should have suicient capacity to deliver the mixture at temperatures above about 400 F. to the flash chamber, while cooler 28 should be capable of reducing the temperature of the product from approximately 400 to 450 F. to about 150 to 250 F. The recycle system. containing recycle pump 18, tubular reactor 21 and attendant piping must be designed to meet process conditions. Specifically, pump 1S should be capable of recycling the mixture at a rate which is 10 to 200, or preferably 20 to 40, times the charge rate into the flash chamber from line 15. The piping associated with the recycle system including the tubular reactor should be small enough to maintain turbulent ow conditions during the period of time when the mixture is in intimate contact with the oxygen-containing gas. Pipe or tubing having an ID of l to 3 is usually satisfactory to produce the turbulent flow required. The length of the tubular reactor is dependent upon the contact time required per pass through the tubular reactor, which is in turn dictated by the recycle rate, the oxidation reaction rate and the viscosity increase desired. For example, when a 1:1 tallowresidual oil mixture is being processed to effect a viscosity increase of to 15 seconds Saybolt Universal at 210 F., a recycle rate of approximately 20:1 and a contact time of about 4 seconds per pass was found to produce the desired viscosity increase. Contact time in this instance is defined as the period of time that the mixture of saponiable material and mineral lubricating oil is in intimate contact with the oxygen-containing gas while flowing under turbulent llow conditions through the tubular reactor.

Temperature and pressure conditions in the tubular reactor may vary somewhat but must be selected to produce the required viscosity change. Thus, the pressure should be superatmospheric, preferably in the range of to 100 p.s.i.g. while temperatures in the range of 300 to 700 F. are often necessary, although temperatures in the range of 400 to 500 F. are preferable.

The rate at which the oxygen-containing gas is injected into the recycle system is dependent upon the recycle rate and the particular oxygen-containing gas being utilized. For example, when air is serving as the oxygen-containing gas, injection rates of 0.02 to 0.20 s.c.f./lb. of mixture circulating through the tubular reactor will be required. An air injection rate of 0.04 to 0.08 s.c.f./lb. of mixture being circulated is preferred.

The reduced pressure maintained in the ash chamber must be suicient to remove excess gases from the chamber and undesirable entrained or dissolved gases from the reaction mixture. Usually a slight vacuum maintained in the ash chamber is sufficient for these purposes, although a pressure 15 to 80 p.s.i. below that in the tubular reactor is satisfactory.

The following example is illustrative of the continuous oxidation of a mixture of saponiiiable material and lubricating oil carried out in accordance with this invention.

EXAMPLE I A mixture of saponiiiable material and lubricating oil was oxidized by the method of this invention as described below.

The equipment employed in the process comprised a tubular reactor, a Iiiash chamber, a charge heater and product cooler with auxiliary piping and pumping equipment for circulating the mixture through the equipment as shown in the drawing. The ash chamber consisted of a 51/3 foot section of 12 inch, schedule 40 stainless steel pipe mounted in a vertical position. The tubular reactor was constructed from a 461/2 foot section of 1% inch schedule 8O stainless steel pipe formed into a coil and mounted in a 4 foot section of 20 inch pipe which served as a heating jacket. Intermediate piping connecting the principal vessels and pumps comprised 1/2 to 2 inch schedule 40 stainless steel pipe. The charge pump was a piston metering pump having a nominal capacity of 1 gallon per minute. The recycle pump was a motor driven centrifugal pump having a nominal capacity of 2O g.p.m. at a head of 150 feet H2O. The vapor space in the flash chamber was connected through a 2 inch stainless steel pipe to a steam vacuum jet equipped with a condenser.

The saponia'ble material employed was a commercial high acid hard tallow having a saponication number of 196, a free fatty acid content of 66% and an iodine number of about 52. The lubricating oil employed was a parain base crude residuum having an API gravity of 23.3 and a Saybolt Universal viscosity at 210 F. of about 176 seconds.

A 50/ 50 weight mixture of tallow and residuum was charged to vessel 10 and maintained at a temperature of approximately 150 F. A stream of the mixture was delivered to preheater 14 by charge pump 12 at a flow rate of approximately 1 g.p.m. The mixture was heated in the charge preheater to approximately 430 F. and flowed from there to flash chamber 17 passing through pressure regulating valve 16 which maintained a pressure of 30 p.s.i.g. on the charge line. The vapor space in the flash chamber was maintained at a pressure of about 13 p.s.i.g. by the steam vacuum jet. The reaction mixture was circulated through tubular reactor 21 by recycle centrifugal pump 18 at a tow rate of approximately 20 gpm. Air at a rate of 10 standard cubic feet per minute and a pressure of p.s.i.g. was injected into line 20A at the entrance to the reaction coil. The mixture of air and saponifable material in oil flowed through the reaction coil under turbulent ow conditions, i.e., at a Reynolds number, fbased on superficial velocity, of approximately 7,280 for the gas phase and approximately 29,790 for the liquid phase. Passage through the tubular reactor caused a partial oxidation of the liquid mixture. The temperature of the liquid mixture was controlled by regulating the Iflow of the heat transfer medium so that the liquid mixture left the reaction coil at a temperature in the range of 460 to 490 F. The reaction mixture was returned to the ash chamber through line 22 and pressure control valve 23 which maintained a pressure of approximately 30 p.s.i.g. in the recycle circuit. Excess air and gases from the reaction were removed in the flash chamber because of the reduced pressure in the vapor space. The oxidized product was removed in a side stream from the pump discharge upstream from the air injection point. The product stream owed at a rate of about 1 g.p.m. through product cooler Z8 where the temperature was reduced to approximately F.

Under these process conditions it was found that at an average tubular reactor temperature of about 464 F. a viscosity increase of 8.8 seconds Saybolt Universal at 210 F. was produced while at an average reactor temperature of 500 F. the viscosity increase amounted to about 13.3 seconds. Tests on the oxidized mixture product for an average tubular reactor temperature of 500 F. showed a viscosity after oxidation of 80.9 SSU at 210 F., a 13.3 second increase over the original viscosity, and a saponitication number of 96 on the product.

The above tests show that a mixture of saponiable material and mineral lubricating oil can be oxidized to produce the desired viscosity increase by the continuous method of our invention. The total residence time in the equipment used for practicing our invention was about 30 minutes although the tot-al contact time in the tubular Ieactor was only 80 seconds (4 seconds/pass, 20:1 recycle ratio). If this oxidation were conducted in a commercial batch kettle process, the required viscosity increase would be achieved by air blowing the mixture for seven to twelve hours at 480 to 485 F. Not only is the batch process more time consuming, but there is a substantial loss of material from the product during the air blowing portion of the operation. Such losses are greatly diminished in our continuous method.

The oxidized mixture prepared by the method of our invention was compared to that produced by the conventional batch process by evaluating sodium soap greases prepared from each )of two oxidized mixtures. Both mixtures were saponified, dehydrated and blended with oil in similar fashion. The greases made from the continuously and the batch oxidized compounds were found to have essentially equivalent properties when a No. 2 grease -Was prepared as shown by the table below.

Continuously Batch Oxidized Oxidized Properties of N GLI N o. 2 Grease Mixture Mixture Sodium Soap Content, Wt. Percent 14. 7 14. 1 Penetration at 77 F Unworked-.- 272 263 Worked 292 282 Dropping Point, F 420 423 such limitations should be imposed as are indicated in the following claims.

We claim:

1. In the preparation of a sodium soap thickened grease by a method which includes oxidizing a mixture of a mineral lubricant oil and a saponiable fatty acid material to increase the viscosity of the mixture prior to saponifying the mixture, the saponiiiable material having an iodine number below about 8O and a free fatty acid content of about 40 to 80% by weight, and consisting essentially of higher fatty acid and higher fatty acid glyceride, the improvement which comprises:

continuously passing a stream of the mixture at a temperature in the range of 400 to 500 F. and superatmospheric pressure and an oxygen-containing gas through a tubular reaction zone under turbulent ow conditions for a period of time suiiicient to obtain a viscosity increase of e35 seconds Saybolt Universal at 210 F.

2. A process according to claim 1 including the following additional step:

(a) passing the oxidized liquid and gas through a separation zone having a vapor space maintained at a pressure substantially lower than the pressure in the reaction zone.

3. The process of claim 1 wherein the saponiable material comprises fatty acid materials selected from the group consisting of C16 18 fatty acids, their glycerides and mixtures thereof.

4. The process of claim 1 wherein the said saponiiiable material is tallow having an iodine number in the range of 40-70 and comprising 50 to 70% free fatty acid con-- tent by weight.

5. In the preparation of a sodium soap thickened grease by a method which includes oxidizing a mixture of a mineral lubricating oil and a saponiable fatty acid material to increase the viscosity of the mixture prior to saponifying the mixture, the saponiable material having an iodine number below about 80 and a free fatty acid content of about 40 to 80% by weight, and consisting essentially of higher fatty acid and higher fatty acid glyceride, the improvement which comprises:

(a) continuously passing lthe mixture at a temperature in the range of 400 to 500 F. into a reduced pressure zone,

(b) then continuously passing the mixture from the reduced pressure zone through a tubular reaction zone at a rate which is between and 40 times the rate at which the mixture is passed into the reduced pressure zone,

(c) continuously returning the mixture from the tubular reaction zone to a vapor space in the reduced pressure zone,

(d) continuously introducing an oxygen-containing gas into intimate contact with the mixture in the tubular reaction zone at a point and a rate sufficient t-o effect a partial oxidation of the mixture which will result in an increase in the Viscosity of the mixture, the mixture and the gas passing through the tubular reaction zone under turbulent flow conditions,

(e) continuously withdrawing vapors from the reduced pressure zone at a -rate sufficient to maintain the reduced pressure, and

(f) continuously withdrawing an oxidized product from the reduced pressure zone at a rate suiiicient to maintain a substantially constant liquid level in the reduced pressure zone,

the contact time between the mixture and the oxygencontaining gas in the tubular reaction zone being sutilcient to effect a viscosity increase of 5 to 35 seconds Saybolt Universal at 210 F. in the oxidized product.

6. In the preparation of a sodium soap thickened grease by a method which includes oxidizing a mixture of a mineral lubricating oil and a saponiable fatty acid material to increase the viscosity of the mixture prior to saponifying the mixture, the ratio of lubricating oil to saponiable material being about 1:2 to 2:1 by weight, the lubricating oil having a viscosity of about 100 to 300 seconds SSU at 210 F. and the saponiiiable material having an iodine number below about 80 and a free fatty acid content of about 50 to 70% by weight, and vconsisting essentially of higher fatty acid and higher fatty acid glyceride, the improvement which comprises:

continuously passing a stream of the mixture at a temperature in the range of 400 to 500 F. and superatmospheric pressure and an oxygen-containing gas through a tubular reaction zone under turbulent ilow conditions for a period of time sufficient to obtain a viscosity increase of the mixture of 5-35 seconds Saybolt Universal at 210 F.

7. A method according to claim 6 `wherein the mineral lubricating oil is a parafnic residual oil having a viscosity of about 15() to 200 seconds Saybolt Universal at 210 F., the saponiable material consists -of tallow fatty acids `and tallow having an iodine number in the range of 40 to and a free fatty acid content of about 50 to 70% by weight, the ratio of lubricating oil to saponifable material is about 1:1 by weight, the oxygen-containing gas is air and the viscosity increase of the mixture is about l0 to 2O seconds Saybolt Universal at 210 F.

References Cited UNITED STATES PATENTS 2,916,453 12/1959 Nelson 252-41 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl. X.R. 252-41, 55

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,474,034 October 21, 1968 Herbert J. Pitman et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column l, line 6l, "1,996,821" should read 1,966,821 Column 6, line l, "p.s.i.g." should read p.s.i.a. Column 7= line 6, "lubricant" should read lubricating Signed and sealed this 8th day of December 1970.

(SEAL) Attest: y

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

